In the First World War, the Dutch-Belgian border was not an ordinary national boundary. South of the border there was war, while to the north lay the peaceful, neutral Netherlands. The Germans army did not initially invest very heavily in the defence of this northern border, as an attack from the neutral Netherlands seemed unlikely. The Germans did have some concerns, however; what if the Allied forces should choose to invade Belgium from Zeelandic Flanders? 

Blog: A Line of Bunkers Along the Dutch Border